A touch panel has been known as an interface for a user to input information to a display device. Arrangement of a touch panel on a screen of a display device permits a user to operate input buttons and icons displayed on the screen, by which information can be readily input to the display device. For example, a stacked-type display device in which a touch panel is mounted on a liquid crystal display device is disclosed in Japanese patent applications No. 2001-154178 and 2001-117719.